Process of drying nitrocellulose



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.F. G. DU -PONT, PROUESS 0F DRYING NITROUELLULOSE- No. 516,924. PatentedMar. 20, 1894.

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UNITED A STATES PATENT OFFICE.

FRANCIS G. DU PONT, OF WILMINGTON, DELAWARE.

PROCESS OF DRYING NITROCELLU LOSE.

SPECIFICATION forming part of Letters Patent No. 516,924, dated March20,1894. pp ion filed June 15,1893. Renewed February 23,1894. SerialNo.501,288. (No specimens-l To all whom it may concern.-

Be it known that I, FRANCIS G. DU Pour, a citizen of the United States,residing at Wilmington, in the county of New Castle and State ofDelaware, have invented certain new and useful Improvements in Processesof Drying Nitrocellulose; and I do hereby declare the following tobe afull, clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

My invention relates to processes for drying ni'tro-cellulose, andparticularly that form thereof known as gun cotton, and it consists inan improved process for accomplishing this purpose by placing the wetgun cotton in a still filled with some volatile oil,and then distillingthe oil and the water contained in the fiber of the gun cotton, whichwill hereinafter be fully described, and particularly pointed out in theclaims.

Gun cotton has always been an exceedingly difficult material todry, forthe reason that the process of drying by the mere application of heat isvery dangerous, and accidents constantly take place when it isattempted. Gun cotton when Wet is absolutely safe. It can only beexploded by specially prepared primers. It can be burned without danger,and no special'care need be taken in storing it. But when gun cotton isdry, the case is entirely different. Dry gun cotton is very dusty, andthe particles of it flying through the air are apt to explode from veryslight, and apparently insignificant causes, such as an electric sparkcaused by the hand touching a piece of metal. These particles lodge atevery point and crevice, and render necessary the greatest care to avoidaccidents, which yet frequently happen.

I have discovered that gun cotton can be dried by placing the wetmaterial in a still filled with volatile oil, such as kerosene orbenzine, and then vaporizing the oil. If the boiling point of the oilused be lower than that of water, the water in the fiber of the guncotton will be carried off mechanically by the particles of vaporizedoil; but if the boiling point of the oil beabout that of water, the twowill be vaporized together. It is preferable to have the boiling pointof the oil at about 212 Fahrenheit, as the distillation then takes placemore uniformly and rapidly than when the oil has a lower boiling point.The dry gun cotton obtained is impregnated with the oil'in which it hasbeen placed, but this does not prevent the use of the same for manyimportant purposes, such as for the manufacture of blasting gelatine byadmixture with nitro-glycerine, or the manufacture of collodion varnishby mixture with ether, or for usev in'the manufacture of celluloidarticles, and for treatment with solvents in all processes in which drygun cotton is necessary, though I do not restrict myself to these uses.By

this process of drying gun cotton, all dust is avoided, and the productis collected in a compact form, and in a condition which renders it lessliable to cause accidents than the common dry gun cotton. By observingthe amount of water driven off in the course of distillation, it iseasy-to determine when all of the water has been driven off; or the guncotton may be left with any desired degree of moisture therein, if it iswished to leave the same slightly wet.

In the drawings accompanying and forming a part of this application, Ihave represented a form of still that is especially fitted for use inthis process, although I do not limit myself to carrying out my processwith this particular form of still, mentioning it merely as a convenientform. I have made separate application for Letters Patent of the UnitedStates for this still, said application having been filed April 13,1893, and serially numbered 470,347. The feature of the same whichrenders it especially applicable to the use suggested is that it permitsan automatic return to the main still of the oil driven off from thesame, while enabling an accurate determination of the amount of waterdistilled off to be made. The use of large quantities of oil is thusrendered unnecessary, and the care which has to be taken with theapparat'us is much lessened.

Before proceeding with a description of my process, I willdes'cribe theapparatus used in carrying it out.

Referring to the drawings, A represents the still, which is of anyconvenient size and construction, and has around its lower portion, B,an encircling steam jacket, provided with steam inlet and outlet pipes.The pipe 0, at

the apex of the conical bottom of the still, serves for the introductionand removal of material. The still is provided with a conical top, D,around the outer shell, F, of which is placed the jacket G, which isprovided with water inlet and outlet pipes, and between which, and thesaid shell F, a stream of cold water is constantly flowing when thestill is 1n operation. The outletH is for the conduction of vaporsescaping from the still to a suitable condenser, which is so arrangedthat the fall of the pipes leading to the same is backward into thestill, so as to drain condensed products into the still-head. Inside ofthe shell F, and of a form corresponding to that of said shell, issuspended the inner shell or cone E, the function of which is to preventthe distillate coming from the conden from falling again into the still,and to determine its delivery, as well as that of all the vaporscondensed in the still-head, i t the annular trough I, which surroundsthe interior of the still at the base of the stillhead. The pipe Jaffords an exit from this trough into the outer vessel K, which answersas a reservoir for the distillate. This reservoir has a conical bottom,and a pipe at the apex of the same, from which may be drawn from time totime the water which collects in the same, the water being heavier thanthe oil. The said reservoir is also provided with an air-tight closureat its top, and a stop cock M for the admission of air. Besides theconnection afforded by pipe J, the reservoir is also connected with thestill by the overflow pipe L, which is joined to the still at a point alittle above the level of the contents of the same, and enters thereservoir at a point below the level of discharge of the distillate,thus allowing the oil, which in this case is the lighter product ofdistillation, to flow back into the main still as rapidly as formed.Cocks are provided in the two pipes connecting the still and thereservoir, so that 1n case a vacuum is used in connection with theoutlet pipe of the still, they may be closed, and air admitted to thereservoir through the cock M, restoring atmospheric pressure, and

"enabling the heavy liquid at the bottom of the reservoir to be drawnofi from time to time as needed.

Proceeding now with my process, I place in the still about two hundredgallons of a suitable volatile oil, such as kerosene or benzinc, and Iprefer to have the boiling point of this oil at about 212 Fahrenheit, asthereby the water in the fiber of the gun cotton is more uniformly andmore rapidly removed. I now place in the still about two hundred poundsof gun cotton, in a state of pulp, which, having been drained of itssurplus water, contains about fifty percent. of its weight of water.Avacuum pump is preferably connected to the pipe H, in order to keep thecontents of the still at a low temperature, which is an advantage. Steambeing now circulated through the steam jacket, distillation commences.The vapors produced rise to the conical top of the still, and a portionof the same will be condensed on the inner side of shell E, and will bysaid shell be delivered into the annular trough I, from whence it willbe conveyed to the reservoir K by pipe J. The uncondensed portion of thevapors passes under the edge of the inner cone, and up between the outerand inner cones. Since the outer cone is surrounded by cold water, afurther and much greater condensation-takes place here, this portion ofthe distillate, like the preceding, being delivered into the reservoir Kby pipe J. If any uncondensed vapor remains, it passes upward throughpipe H into the condenser, and is there condensed, whence it finds itsway. into the annular trough I, and from thence, by pipe J, into thereservoir K. All of the distillate is thus condensed, collected in theannular trough, and delivered into the reservoir. When the distillatereaches the reservoir, a separation of the products forming the same"takes place, the heavier product of the same, water, falling to thebottom of the reservoir, and the lighter product, oil, (after the levelof the contents of the reservoir has reached that of the pipe L,) passingover into the main still. The quantity of water collected is aconstant index of the amount dried out of the gun cotton, because it iseasy to ascertain the average amount of water that is contained in theoriginal gun cotton. This water should be drawn off from time to time,in order that its level may not rise to that of the pipe L, and thusWater be returned to the still. While this operation is being performed,the cooks to pipes J and L should be closed, and the cock M opened, sothat the ordinary atmospheric pressure may exist in the reservoir. Whenno more water collects in the reservoir, the process is finished, andthe contents of the still are drawn off, the surplus oil being drainedofi from the gun cotton. The gun cotton is now in condition to be usedfor any processin which the presence of oil is not objectionable.

The process maybe carried on with alighter oil in the still, but in suchcase the operation of removing the water in the still is necessarilyslower, as the temperature is not so high, and the water comes over moreslowly, most of it being carried mechanically by the vapoized oil, sothat if it isdesired that the fiber of the gun cotton should beimpregnated with a lighter oil, it is preferable to accomplish this bypercolation, after the process of drying the gun cotton has beenfinished. If such lighter oil is used, the process of carrying off thewaterisfirstone of evaporation,andthen of mechanically carrying over thewatery vapor with the vapor of the low boiling oil. For instance,takeanoilwhichboils at75centigrade. This is considerably below the boilingpoint of water, and yet when water, mixed with gun cotton, is placed insuch an oil, the vapor of the water is carried 01f rapidly by the vaporof the oil. A very volatile oil will of course carry ofi the oil tooslowly, and there is a limit at which the process will go on too slowlyfor practice. This limit may be set at about 50 centigrade, although theprocess may possibly be carried on at a lower temperature. The quantityof oil evaporated has nothing to do with the economy of the process,except in loss of time, because the oil is constantly returned to thestill, separate from its water, and the process can go on in acontinuous cycle. While it is thus true that when oils are used whoseboiling point is lower than that'of water, the removal ofthe Water takesplace very slowly, the reverse is the case when oils are used whoseboiling points are higher than that of Water. In this case, the processwill go on very rapidly, but here arises a consideration which does nothold with oils of low boiling point. Suppose for instance that I use anoil Whose boiling point is 120 centigrade. When the still is heated, thewater in the gun cotton will keep the boiling point down as long as itis coming off, but as the quantity of water in the gun cotton becomesless and less, the boiling point will continually rise; so that when thecotton is dry, it will be heated up to the temperature of the oil, atemperature which is detrimental to its stability. This does not,however, prevent the drying in oils of even a very high boiling point.

In case an oil is used which has a greater specific gravity thanwater,it Will sink to the bottom of the reservoir, and the water willrise to the top of the same. The oil is returned in such case byextending the branch of the pipe L which extends into the reservoir tothe bottom of the same.

- *Ido not confine myself to the use of kerosene, or benziue as the oilin which to place the gun cotton for removal of the water contained inits fiber, but use for that purpose any volatile oil that is found to besultable; nor do I confine myself to the use of my process in drying guncotton, for I may dry by it other forms of nitro-cellulose.

What I claim as new, and desire to secure by Letters Patent, is-

1. The process of drying nitro cellulose which consists in placing thewet nitro-cellulose in a volatile oil, vaporizing the oil, and therebyremoving the water in thefiber of the nitro-cellulose, substantially asdescribed.

2. The process of drying nitro cellulose which consists in placing thewet nitro-cellulose in a hydro-carbon oil, vaporizing the oil, andthereby removing the Water in the fiber of the nitro-cellulose,substantially as described.

3. The process of drying nitro cellulose which consists in placing theWet nitro-cellulosein kerosene, vaporizing the oil, and thereby removingthe water in the fiber of the mtro-cellulose, substantially asdescribed.

4. The process of drying nitro cellulose which consists in placing thewet nitro-cellu lose in kerosene oil having a boiling-point of I,

212 Fahrenheit, vaporizing the oil and the water in'the fiber of thenitro-cellulose, and thereby drying the nitro-cellulose,substantially asdescribed. 4 i

In testimony whereof I affix my signature in presence of two witnesseslFRANCIS G. DUPONT. Witnesses:

THOS. J. BOWEN, Jr.,

LEONARD E. WALES, J r.

